Transform Drawing using GCPs
Rubber sheeting with GCPs given in CSV.
Often, CAD users have a drawing in one coordinate system and want to transform it into another. The best and easiest way is to acquire points for which the coordinates are known in both coordinate systems. These points can be called ground control points (GCPs). The following graphic shows three of such points that we can use for transformation.
CSV File Format for GCP Input in SPCAD
SPCAD offers a custom transformation tool that allows users to transform drawing coordinates from one system to another using Ground Control Points (GCPs) in a CSV file. The CSV file should be formatted with five columns:
- Y coordinate of the target coordinate system Each row represents one GCP.
- Serial Number of the GCPs
- X coordinate of the source coordinate system
- Y coordinate of the source coordinate system
- X coordinate of the target coordinate system
Each row in the CSV file corresponds to one GCP.
Parameter Helmert Transformation
SPCAD utilizes a 4-parameter Helmert transformation that preserves the shape of the features while performing translations in the x and y directions and applying rotation and scaling. A key feature of SPCAD is its ability to display the residual error for the set of GCPs, allowing users to assess the quality of the provided GCPs.
In the following figure we have survey data in the Lambert Conformal conic based coordinate system. and we want it to be in related UTM coordinates system.
SPCAD reads the CSV and computes the residuals.
After the user is satisfied and presses OK, the features are transformed, and a prompt is given to type the name of the transformed drawing, which is then saved in the user-specified folder.
The transformation of drawings implemented by SPCAD is also considered as rubber sheeting. It employs GCPs to spatially adjust and rectify drawings, adjusting translation in both directions, rotation, and scale, similar to rubber sheeting techniques.
